The present invention relates generally to the field of non-invasive imaging and, more specifically, to the field of medical imaging using Computed Tomography systems.
Computed Tomography (CT) imaging systems measure the attenuation of X-ray beams passed through a patient from numerous angles. Based upon these measurements, a computer is able to reconstruct images of the portions of a patient's body responsible for the radiation attenuation. As will be appreciated by those skilled in the art, these images are based upon separate examination of a series of angularly displaced projection images. It should be pointed out that a CT system produces data that represents the line integral of linear attenuation coefficients of the scanned object. This data is then reconstructed to produce an image which is typically displayed on a cathode ray tube, and may be printed or reproduced on film. A virtual 3-D image may also be produced by a CT examination.
CT scanners operate by projecting fan shaped or cone shaped X-ray beams from an X-ray source that is collimated and passes through the object, such as a patient, that is then detected by a set of detector elements. The detector element produces a signal based on the attenuation of the X-ray beams, and the data are processed to produce signals that represent the line integrals of the attenuation coefficients of the object along the ray paths. These signals are typically called projections. By using reconstruction techniques, such as filtered backprojection, useful images are formulated from the projections. The locations of pathologies may then be located either automatically, such as by a computer assisted diagnosis (CAD) algorithm or, more conventionally, by a trained radiologist.
However, CT detectors may not provide sufficient resolution to accurately resolve structures on the order of 0.5 to 1.5 mm, which may still be of diagnostic and pathological interest. This lack of resolution may be problematic in applications where greater resolution is desired, such as inner ear imaging, cardiac and vascular imaging, small animal imaging, and oncological screening.
In addition, it is often desirable to image large volumes inside the body while maintaining a desired X-ray dosage. For example, in cardiac CT imaging it is generally desirable to capture the entirety of the heart in one rotation of the scanner. Likewise, in whole-organ perfusion assessment it is generally desirable to capture the entire organ within a single rotation. However, other CT imaging applications may not require as extensive a field of view and, indeed, there may be scanning speed benefits associated with a smaller field of view. Therefore, it may be advantageous to be able to vary the field of view, balancing the desired field of view with the desired scan speed. It may therefore be desirable to provide high resolution in conjunction with a configurable field of view.